Tee junction waveguide circulator having dielectric matching posts at junction

ABSTRACT

A broadband tee junction waveguide circulator of improved design is disclosed. A ferrite element of triangular cross-section is disposed in the region of the junction of the two waveguides. Dielectric matching &#39;&#39;&#39;&#39;posts&#39;&#39;&#39;&#39; extending between the broad walls of the waveguide junction near each of the apexes of the ferrite element provide improved impedance matching. The matching posts present independently adjustable capacitive susceptances to the propagating wave energy in the three arms of the device for matching purposes and minimize higher order mode conversion. Those higher order modes which are generated are below cut-off and decay rapidly. The advantages of this configuration are its light weight, relatively small size and ease of tuning.

nited States Patent 1191 Andrikian Nov. 26, 1974 1 TEE JUNCTIONWAVEGUIDE CIRCULATOR HAVING DIELECTRIC MATCHING POSTS AT JUNCTION [75]Inventor: Charles P. Andrikian, Los Angeles,

Calif. I

[73] Assignee: Hughes Aircraft Company, Culver City, Calif.

[22] Filed: Oct. 17, I973 21 Appl. No.: 407,374

[52] US. Cl.....- 333/l.l, 333/9, 333/98 M [51] Int. Cl. Il0lp 1/32 [58]Field of Search 333/1.l, 9, 98 M [56] References Cited UNITED STATESPATENTS 3.231.835 1/1966 Nielsenvet a1, 333/l.1 3,337,812 8/1967 Webb333/l.l UX 3,350,664 10/1967 Pistilli et a1. 333/1.1 3,466,571 9/1969'CONDUCTIVE PEDE STAL} Primary li.ramt'ner-Pau1 L. 'Gensler Attorney,Agent, or Firm-W. H. MacAllister, Jr.; D. O. Dennison [57] ABSTRACT Abroadband tee junction waveguide circulator of improved design isdisclosed. A ferrite element of triangular cross-section is disposed inthe region of the junction of the two waveguides. Dielectric matchingposts extending between the broad walls of the waveguide junction neareach of the apexes of the ferrite element provide improved impedancematching.

The matching posts present independently adjustable capacitivesusceptances to the propagating wave en ergy in the three arms of thedevice for matching purposes and minimize higher order mode conversion.Those higher order modes which are generated are below cut-off and decayrapidly. The advantages of this configuration are its light weight,relatively small size and ease of tuning.

6 Claims, 2 Drawing Figures i DIELECTRIC SLAB GYROMAGNETIC MATERIALPmmmv 3.851279 Fig. 1.

CONDUCTIVE H DIELECTRIC PEDESTALN f SLAB DIELECTRIC POST ,w- IO TEEJUNCTION WAVEGUIDE CIRCULATOR HAVING DIELECTRIC MATCHING POSTS ATJUNCTION FIELD OF THE INVENTION This invention relates generally toferrite devices and more particularly to broadbandteejunctionwaveguidecirculators.

DESCRIPTION OF THE PRIOR ART "tors or switching means. In the past, alarge number of such means have been proposed and used, some of whichhave been acceptable for most applications. Probably the mostasuccessfulcirculators and switches for use in the microwave spectrum employ anelement of gyromagnetic material such as a ferrite. Commonly,thismaterial is disposed in the junction of one ormore sections ofwaveguides through which the microwave energy is propagated. Bycreatinga magnetic flux field through this element there will be a gyromagneticeffect which may be effectively utilized to control they microwaveenergy in the desired manner.

Unfortunately,.the presence of such a gyromagnetic element in awaveguide causes a change in the impedance of the'junction through whichthe electromagnetic energy ispropagated. The resultant mismatching ofimpedances, in turn, causes standing waves and other losses to occur inthe device. In an effort to overcome this effect many schemes have beenproposed to match the impedance of the section of waveguide'containingthe ferrite with the surrounding portions of the waveguides. Since theequipment utilizing such devices is required to operate over arelatively wide band of frequencies it is desirable that the devicesthemselves have broadband frequency response characteristics. In otherwords, the impedance match of the device must be within acceptablelimits over a relatively broad range of frequencies.

space limitations are important it is desirable to use waveguidecirculators of other than the Y-junction variety. For example, becauseof the fact that the arms of the Y-junction circulator are mutually lapart, it is generally necessary to provide additional waveguide bendsat at least two of the ports of the junction. Due tothis fact, it isdesirable to use circulators of the tee junction variety. When this isdone, however, the inherently asymmetrical geometry of the tee junctiongives rise to much greater problems of impedance matching, particularlyimpedance matching over frequency ranges comparable to those obtainablewith circulators of the Y-junction variety.

Due to symmetry, Y-junction waveguide circulators generally utilizeidentical matching obstacles in all three ports. However, because thetee junction is asymetrical matching obstacles of different values aregenerally required. Theproblem then.is one of obtaining matchingobstacles whose values can be adjustedwithout substantial interactionwith the other obstacles. The feature of independently adjustablematching obstacles also allows greater design freedom and relaxedmanufacturing tolerances.

Accordingly, it is a general object of the present invention to providean improved waveguide circulator of the tee junction type havingbroadband characteristics. I It is another object of the presentinvention to provide a tee junction circulator having independentlyadjustable matching obstacles.

SUMMARY OF THE INVENTION It is therefore proposed, in accordance withthe present invention to provide tee junction waveguide circulators inwhich the energy may be controlled more uniformly over a considerablygreater bandwidth. More particularly, this is accomplished not only byutilizing the proven impedance matching and broadbanding techniquesemployed with Y-junction circulatorsj but by also including uniquedielectric matching structures for the gyromagnetic element, Thesetechniques include the mounting of the gyromagnetic element within thejunction formed by the constituent waveguides between metallic pedestalsand insulating members and by also including dielectric posts'in thevicinity of the corners of the triangular gyromagnetic element. The useof dielectric posts rather than other impedance matching obstaclesminimizes the generation of higher BRIEF DESCRIPTION OF THE DRAWINGS Theabove-mentioned and other features and objects of this invention willbecome more apparent by reference to the following description taken inconjunction with the accompanying drawings, in which like referencenumerals correspond to like structural elements and, wherein:

FIG. 1 is a partially broken-away pictorial view of a preferredembodiment of the present invention; and

FIG. 2 is a cross-sectional plan view of the embodiment of FIG. 1. l

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring more specifically tothe drawing, FIG. 1 is a partially broken-away pictorial view of a teejunction waveguide circulator according to the present invention. InFIG. 1 three sections of rectangular conductively bounded waveguide 10,11 and 12 meet in a common Hplane tee junction. Waveguide sections 11and 12 are arrangedcoaxially and can comprise, for example, a singlerectangular waveguide. Waveguide section 10 abuts waveguide sections 11and 12 at a right angle to form the junction. Disposed within thejunction in a manner to be discussed in greater detail hereinbelow is atriangular slab-like gyromagnetic element 13, together with itstriangular matching and supporting structures.

The supporting structure for element 13 comprises an upper conductivepedestal 14, a lower conductive pedestal l5, and upper and lowerdielectric slabs 16 and 17, respectively. Conductive pedestals I4 and 15are jointed and conductively bonded to the upper and lower broad wallsof the junction, respectively. Upper and lower dielectric members 16 and17 provide insulating support for element 13 and can be convenientlybonded in place by means of a suitable low-loss adhesive. The compositestructure, therefore, resembles a triangular shaped, multi-layersandwich with gyromagnetic element 13 being sandwiched betweendielectric elements 16 and 17 and this combination, in turn, beingsandwiched between conductive pedestals l4 and 15.

In practice, dielectric members 16 and 17 can be fabricated ofdielectric material such as Teflon having a dielectric constant on theorder of 2.1. An external magnetic field generated, for example, by apermanent magnet or by a suitably energized electromagnet is directedthrough the gyromagnetic element in a direction perpendicular to thebroad wall of the junction. As shown in FIG. 1, the magnetic field H isdirected from above. However, as is well-known in the art, this fieldcan be reversed, thereby reversing the direction of energy circulation.

Although the broadbanding characteristics of the composite pedestal,dielectric member, gyromagnetic element struture of FIG. 1 iswell-known, it has been found that in circulators of the tee junctionvariety, mismatches and narrow band operation can still occur. With thetee junction circulator of FIG. 1, therefore, additional impedancematching obstacles are employed. These obstacles comprise dielectricposts 18, 19 and 20 which are disposed near the apexes of element l3 andits composite supporting structure. Dielectric posts 18, 19 and 20, inthe shape of right circular cylinders, extend across the interior of thewaveguide junction between the broad walls thereof. In general, thedielectric constant of dielectric posts 18, 19 and 20 should berelatively high, on the order of nine to 15. These limits, however. arenot absolute but rather represent a good design compromise.

Dielectric posts 18, 19 and 20 present a capacitive susceptance to thewave energy propagating within the guides. The value of the respectivecapacitive susceptance is a functiotn of the dielectric constant of thematerial, the diameter of the posts, and their location within thejunction. In general, a higher dielectric constant allows a smaller postdiameter. Lower dielectric constant and correspondingly greater postdiameter may give rise to undesirable multimode effect. Higherdielectric constants and correspondingly smaller post diameters. on theother hand, may result in posts which are more fragile than desirable.In any event, once located, posts 18, 19 and 20 can be bonded in placeby a suitable low loss adhesive such as epoxy resin.

Referring now to the cross-sectional view of FIG. 2, the arrangement ofthe dielectric posts 18, 19 and 20 is shown, together with the locationof gyromagnetic element 13 within the tee junction. Element 13 ispreferably disposed within the junction with one apex thereof coincidingwith the axis of waveguide section 10. The opposite side of thegyromagnetic element extends parallel to the axes of waveguide sections11 and 12 and may be slightly displaced therefrom in the direction ofwaveguide section 10. Also the planar top and bottom surfaces of element13 are parallel to the top and bottom broad walls of the junction. Thelocation of element 13 in this manner is to approximate as nearly aspossible symmetrical loading to the wave energy in all three of thewaveguide sections forming the junction. Dielectric posts 18, 19 and 20are individually disposed adjacent each of the apexes of triangularelement 13.

The optimum position for each of the dielectric posts l8, l9 and 20 canbe conveniently obtained experimentally. In general, for a given postdiameter and dielectric constant, the proper phase position of thecompensating capacitive susceptance is found by varying the position ofthe post longitudinally along the direction of its adjacent waveguideaxis (e.g., to the right or left for ports 18 and 19). The magnitude ofthe capacitive susceptance presented by the post is adjusted by varyingthe post position transversely to the waveguide section. The optimumspacing between the apexes of element 13 and its corresponding post is avery small fraction of a wavelength of the propagating wave energy.

In operation, it is assumed that the tee junction circulator of FIG. 1is interconnected in a microwave circuit by flange couplers or othermeans well-known in the art. In a typical application waveguide section11 may be coupled to a source of electromagnetic wave energy andwaveguide section 12 may be coupled to a utilization device. Waveguidesection 10 may be coupled to a matching load impedance. Such anarrangement comprises an isolator structure widely used in microwavesystems. The wave energy is thus coupled into waveguide section 11 and,depending upon the direction and magnitude of the magnetic biasing fieldH. out of waveguide section 12 or 10. If it is assumed that thedirection and strength of the magnetic field is such as to cause theenergy to be coupled out ofwaveguide section 12, then any energyentering the junction from waveguide section 12 will be coupled out ofwaveguide section 10 and any energy entering waveguide section 10 willbe coupled out through waveguide section 11.

Other elements such as screws, capacitive irises and metallic buttonshave been proposed for matching purposes. In general, however, theseelements are characterized by conductive discontinuities of the sortwhich give rise to higher order mode conversion. (i.e., modes other thanthe dominant TE mode.) In general, higher order modes are to be avoided.Since the dielectric posts present no discontinuities in the vertical orE- field direction mode conversion is minimized. Any .other higher ordermodes caused by the presence of the dielectric posts l8, l9 and 20 aresuch that they are above cut-off for the waveguide sections l0, l1 and12. Thus, they propagate only a short distance in these waveguidesections.

Tee junction circulators of the type shown in FIGS. 1 and 2 have beenconstructed and operated in the 4 GHz and 6 GHz regions. Such structureshave displayed performance characteristics comparable to broadbandY-junction circulators of the type described in US. Pat. No. 3,104,361cited hereinabove. Such circulators have displayed a bandwidth on theorder of 12 percent measured between the 20 db points. In a typicaldevice design for the 4 GHz region the following approximate dimensionsand parameters were utilized:

TABLE I Waveguide Sections 11 and 12 Section 10 TABLE I-ContinuedGyromagnetic element l3 In all cases it is understood that theabove-described embodiment is merely illustrative of but one of a numberof the many possible specific embodiments which can representapplications of the principles of the present invention. Numerous andvaried other arrangements can be readily devised in accordance withthese principles by those skilled in the art without departing from thespirit and scope of the invention.

What is claimed is:

l. A microwave circulator comprising, in combination:

three rectangular conductively bounded waveguide sections joined to forma common tee junction and having a pair of opposite broad walls at saidjunction;

at least one slab-like element of gyromagnetic material of substantiallytriangular shape disposed within said junction, one apex of saidgyromagnetic element being substantially coincident with the axis of theside arm of said tee junction;

three dielectric elements of substantially solid cylindricalcross-section disposed within said junction, each of said dielectricelements extending between said opposite broad walls with one elementbeing immediately adjacent each of the apexes of said gyromagneticelement; and

means for subjecting said gyromagnetic element to a magnetic fielddirected normal to said broad walls.

2 The circulator according to claim 1 wherein said element ofgyromagnetic material is supported within said junction between a pairof dielectric support members and conductive pedestals.

3. In a microwave circulator structure of the type having three sectionsof rectangular conductivelybounded waveguide sections abutting to forman H- plane tee junction, at least one triangular shaped element ofgyromagnetic material disposed within said junction, means for biasingsaid element with an external magnetic field, and impedance matchingmembers disposed within said junction; the improvement comprising acompletely dielectric post extending across the interior of saidjunction adjacent each apexof said element of gyromagnetic material.

4. The microwave circulator according to claim 3 wherein said posts havea dielectric constant between nine and 15.

5. A microwave circulator comprising, in combination:

first, second and third sections of rectangular, conductively boundedwaveguide, said waveguide sections abutting to form a common H-plane teejunction with said first and second sections extending coaxially andsaid third section extending at a right angle to said first and secondsections;

at least one slab-like element of gyromagnetic material of substantiallytriangular shape disposed within said junction;

at least three dielectric elements of substantially solid cylindricalcross-section disposed within said junction, one of said dielectricelements being adjacent each of the apexes of said gyromagnetic element,and

means for subjecting said gyromagnetic element to a magnetic field.

6. The circulator according to claim 5 wherein one apex of saidgyromagnetic element substantially coincides with the axis of said thirdwaveguide section and the opposite side of said gyromagnetic elementsubstantially coincides with the common axis of said first and secondwaveguide sections.

1. A microwave circulator comprising, in combination: three rectangularconductively bounded waveguide sections joined to form a common teejunction and having a pair of opposite broad walls at said junction; atleast one slab-like element of gyromagnetic material of substantiallytriangular shape disposed within said junction, one apex of saidgyromagnetic element being substantially coincident with the axis of theside arm of said tee junction; three dielectric elements ofsubstantially solid cylindrical cross-section disposed within saidjunction, each of said dielectric elements extending between saidopposite broad walls with one element being immediately adjacent each ofthe apexes of said gyromagnetic element; and means for subjecting saidgyromagnetic element to a magnetic field directed normal to said broadwalls.
 1. A microwave circulator comprising, in combination: threerectangular conductively bounded waveguide sections joined to form acommon tee junction and having a pair of opposite broad walls at saidjunction; at least one slab-like element of gyromagnetic material ofsubstantially triangular shape disposed within said junction, one apexof said gyromagnetic element being substantially coincident with theaxis of the side arm of said tee junction; three dielectric elements ofsubstantially solid cylindrical cross-section disposed within saidjunction, each of said dielectric elements extending between saidopposite broad walls with one element being immediately adjacent each ofthe apexes of said gyromagnetic element; and means for subjecting saidgyromagnetic element to a magnetic field directed normal to said broadwalls.
 2. The circulator according to claim 1 wherein said element ofgyromagnetic material is supported within said junction between a pairof dielectric support members and conductive pedestals.
 4. The microwavecirculator according to claim 3 wherein said posts have a dielectricconstant between nine and
 15. 5. A microwave circulator comprising, incombination: first, second and third sections of rectangular,conductively bounded waveguide, said waveguide sections abutting to forma common H-plane tee junction with said first and second sectionsextending coaxially and said third section extending at a right angle tosaid first and second sections; at least one slab-like element ofgyromagnetic material of substantially triangular shape disposed withinsaid junction; at least three dielectric elements of substantially solidcylindrical cross-section disposed within said junction, one of saiddielectric elements being adjacent each of the apexes of saidgyromagnetic element, and means for subjecting said gyromagnetic elementto a magnetic field.
 6. The circulator according to claim 5 wherein oneapex of said gyromagnetic element substantially coincides with the axisof said third waveguide section and the opposite side of saidgyromagnetic element substantially coincides with the common axis ofsaid first and second waveguide sections.